Wireless communication control method and communication system

Abstract

In order to increase the efficiency of downlink communication, this wireless communication control method includes: a transmission station, to which a first wireless terminal belonging to a first group and a second wireless terminal belonging to a second group different from the first group are connected, transmitting to the first wireless terminal a first signal transmitted at a plurality of timings by continuous transmission using an orthogonal cover code; and the transmission station transmitting to the second wireless terminal a second signal superimposed on the first signal transmitted at a specific timing among the plurality of timings.

Description

Wireless communication control method and communication system

[0001] The present disclosure relates to a wireless communication control method and a communication system.

[0002] 3GPP (registered trademark) has standards for base stations that support Non-Terrestrial Networks (NTN) (e.g., Non-Patent Document 1). 3GPP also has standards related to Non-Orthogonal Multiple Access (NOMA), a technology that enables information to be sent to multiple users in the same frequency band by transmitting signals with varying transmission power (e.g., Non-Patent Document 2).

[0003] 3GPP (registered trademark) TR 38.811 V15.4.0 (2020-09) 3GPP (registered trademark) TS 38.211 V18.1.0 (2023-12), 6.3.1

[0004] An object of the present disclosure is to provide a radio communication control method and a communication system that can efficiently perform downlink communication between multiple radio terminals.

[0005] One aspect of the present disclosure is a wireless communication control method including: a transmitting station connected to a second wireless terminal belonging to a first group and a second wireless terminal belonging to a second group different from the first group, transmitting, to the first wireless terminal, a first signal transmitted at multiple timings by continuous transmission using an orthogonal cover code; and the transmitting station transmitting, to the second wireless terminal, a second signal superimposed on the first signal transmitted at a specific timing among the multiple timings.

[0006] Also, one aspect of the present disclosure is a communication system including a transmitting station to which a first wireless terminal belonging to a first group and a second wireless terminal belonging to a second group different from the first group are connected, the transmitting station including a circuit that executes a process of transmitting, to the first wireless terminal, a first signal that is transmitted at a plurality of timings by continuous transmission using an orthogonal cover code, and a process of transmitting, to the second wireless terminal, a second signal that is superimposed on the first signal that is transmitted at a specific timing among the plurality of timings.

[0007] Aspects of the present disclosure may include a transmitting station, a base station, a satellite station, and a wireless terminal that constitute a communication system according to the present disclosure, as well as a storage medium capable of temporarily storing a program.

[0008] According to the present disclosure, it is possible to efficiently carry out downlink communications between multiple wireless terminals.

[0009] FIG. 1 is a diagram illustrating an example of the configuration of a communication system according to an embodiment. FIG. 2 is a diagram illustrating an example of the configuration of a communication system. FIG. 3A illustrates an example of the configuration of a signal transmitted from a satellite station 2A, FIG. 3B illustrates an example of the configuration of a signal transmitted from a satellite station 2B, FIG. 3C illustrates an example of the configuration of a signal received by a terminal 10a, and FIG. 3D illustrates an example of the configuration of a signal received by a terminal 10b. FIG. 4 is an explanatory diagram of a signal demodulation method using successive interference cancellation (SIC). FIGS. 5A and 5B are explanatory diagrams of a method of demodulating a continuously transmitted signal using an orthogonal cover code (OCC) in terminals 10A and 10B. FIGS. 6A, 6B, and 6C are diagrams illustrating an example of a case where transmission power control (TPC) is performed in continuously transmitted signals using OCC. FIG. 7 is a diagram illustrating an example of the configuration of a wireless device. FIG. 8 is a sequence diagram illustrating an example of message exchange between a terminal station and a base station. FIG. 9 is a sequence diagram illustrating the operation of a communication system. FIG. 10 is a diagram illustrating an example of the configuration of a base station. Fig. 11 is an explanatory diagram of OCC and transmission power control. Fig. 12 is a diagram showing an example of the configuration of a terminal station. Fig. 13 is a flowchart showing an example of processing by a control station. Fig. 14 is a flowchart showing an example of processing by a base station. Fig. 15 is a flowchart showing an example of processing by terminals 10A and 10B. Fig. 16 is a flowchart showing an example of processing by terminals 10a and 10b.

[0010] The sixth-generation mobile communication system (6G) is being considered to ensure communication means anywhere on Earth. NTNs, such as satellite communications, are promising wireless communication networks that will realize the above-mentioned communication means. NTNs are also expected to not only address dead zones in terrestrial networks (TNs), but also improve reliability when combined with TNs and be used for IoT (Internet of Things) communications.

[0011] However, the available frequencies for NTN are limited, and technologies capable of accommodating the expected rapid increase in traffic are required. Furthermore, ensuring the desired communication quality for non-line-of-site (NLOS) terminal stations (hereafter referred to simply as "terminals"), where the distance between the satellite station and the terminal station makes high-gain antennas unusable, is a major issue. In other words, in NTN communications, multiple terminals involved in downlink communications can be classified into those with good link budgets (good margins) and those with poor link budgets (poor margins). The link budget is a method for calculating the overall link balance (allowable propagation loss) by adding or subtracting all gain factors (gains due to antennas, amplifiers, coding, etc.) and loss factors (losses due to cables, free space, fading, thermal noise, etc.) present in the path (link) between the transmitting and receiving ends of the communication system in dB values. Link budget calculations provide the reachability distance from the base station to the terminal, which is used in wireless system circuit design (cell radius and transmission power).

[0012] A communication system according to an embodiment includes a transmitting station connected to a first wireless terminal belonging to a first group and a second wireless terminal belonging to a second group different from the first group, wherein the transmitting station transmits, to the first wireless terminal, a first signal transmitted at a plurality of timings by continuous transmission using an orthogonal cover code, and the transmitting station transmits, to the second wireless terminal, a second signal superimposed on the first signal transmitted at a specific timing among the plurality of timings.

[0013] Hereinafter, a communication system and a wireless communication control method in a communication system according to an embodiment will be described with reference to the drawings. The configurations of the following embodiments are examples, and the present disclosure is not limited to the configurations of the embodiments. Note that, although a 5G (fifth generation mobile communication system) communication system is exemplified in the embodiments, the mobile communication method according to the present disclosure can be applied to wireless communication systems other than 5G, such as 4G (LTE) and 6G.

[0014] 1 and 2 are diagrams showing an example of the configuration of a communication system. In FIG. 1, the communication system includes a plurality of base stations 1 controlled by a control station 3. In the example shown in FIG. 1, base stations 1A and 1B are exemplified as the plurality of base stations 1. Each of base stations 1A and 1B is a ground station. In the example shown in FIG. 1 and 2, the control station 3 is exemplified as a device independent from the base station 1, but a configuration in which any one of the plurality of base stations 1 operates as the control station 3 may also be adopted.

[0015] The communication system also includes multiple satellite stations 2 corresponding to (paired with) multiple base stations 1 (earth stations). In the example shown in FIG. 1 , a satellite station 2A operates as a relay station for base station 1A, and a satellite station 2B operates as a relay station for base station 1B. The satellite station 2 accommodates multiple terminals 10 as its subordinate terminals 10. The satellite station 2 transmits (transfers) signals (information and messages) received from each of the subordinate terminals 10 to the base station 1, and forwards signals including data for downlink communication transmitted from the base station 1 to each of the terminals 10. However, a configuration may also be adopted in which the satellite station 2 generates and transmits signals including data for each terminal 10 in accordance with instructions received from the base station 1. The terminals 10 are referred to as UEs (User Equipment), and the base station 1 is referred to as gNodeBs (gNBs), etc.

[0016] Satellite station 2A has terminal 10a and terminal 10A as its subordinate terminals 10. Satellite station 2B has terminal 10b and terminal 10B as its subordinate terminals 10. As shown in Fig. 2, terminals 10a, 10A, 10b, and 10B are located in an area (interference area) where the coverage area (cell) of satellite station 2A and the coverage area (cell) of satellite station 2B overlap.

[0017] The multiple terminals 10 are classified into a first group and a second group. Among the multiple terminals 10, terminals 10A and 10B with good link budget values ​​(with ample link budget margin) are classified into the first group. On the other hand, terminals 10a and 10b with poor link budget values ​​(with no link budget margin) are classified into the second group. The terminals 10A and 10B are examples of "first wireless terminals," and the terminals 10a and 10b are examples of "second wireless terminals." The satellite stations 2A and 2B are examples of "transmitting stations." Note that the communication system can be configured such that base stations 1A and 1B are directly connected to the multiple terminals 10, in which case the base stations 1A and 1B correspond to "transmitting stations."

[0018] Fig. 3A shows an example of the structure of a signal transmitted from satellite station 2A, Fig. 3B shows an example of the structure of a signal transmitted from satellite station 2B, Fig. 3C shows an example of the structure of a signal received by terminal 10a, and Fig. 3D shows an example of the structure of a signal received by terminal 10b. In order to generate a suitable downlink communication signal while the transmission power of each of satellite stations 2A and 2B is limited, each of base stations 1A and 1B performs the following processing.

[0019] First, the satellite station 2A (2B) reduces the transmission power of the signal addressed to the terminal 10A (10B) while increasing the transmission power of the signal addressed to the terminal 10a (10b) (see Figures 3A and 3B). By increasing the difference in transmission power, the SIR required for demodulation using SIC in the terminal 10 is ensured.

[0020] Second, the satellite station 2A (2B) generates a signal (referred to as an OCC repetitive transmission signal) using an orthogonal cover code (OCC) as a downlink communication signal for the terminal 10A (10B) belonging to the first group. The OCC repetitive transmission signal is a method of repeatedly transmitting a signal a predetermined number of times. In other words, in the repetitive transmission, the signal is transmitted at multiple timings (slots (resource blocks: RBs, one RB is one slot on the time axis)) corresponding to the number of times.

[0021] 3A to 3D, the number of consecutive transmissions is 2, and each timing (slot) is indicated by S1 and S2. The signal transmitted at each of S1 and S2 is multiplied by an OCC (+1 or -1) according to the OCC pattern, resulting in a state with a plus or minus sign.

[0022] For example, as shown in FIG. 3A, in an OCC serial signal addressed to terminal 10A, the signals corresponding to S1 and S2 have a plus sign (+) according to the OCC pattern "+1, +1." On the other hand, as shown in FIG. 3B, in an OCC serial signal addressed to terminal 10B, the signal corresponding to S1 has a plus sign and the signal corresponding to S2 has a minus sign (-) according to a different OCC pattern "+1, -1." The OCC serial signal is an example of a "first signal." The signal superimposed on the OCC serial signal (NOMA signal) is an example of a "second signal."

[0023] In the satellite station 2A (2B), the signal addressed to the terminal 10a (10b) is superimposed on the OCC continuous transmission signal using the same frequency band as the signal transmitted at S1 or S2, which are the multiple transmission timings of the continuous transmission signal. At this time, the SIR required for SIC is ensured, as described above. Here, the satellite station 2A superimposes the signal at S1, and the satellite station 2B superimposes the signal at S2. As a result, as shown in Figures 3C and 3D, the signal addressed to the terminal 10a is received at S1, and the signal addressed to the terminal 10b is received at S2. In this way, signals addressed to four terminals 10 can be transmitted using two slots, thereby improving frequency utilization efficiency.

[0024] FIG. 4 is an explanatory diagram of a signal demodulation method to which successive interference cancellation (SIC) is applied. In NOMA, a receiving station receives a signal in which multiple signals (signals 1 and 2 are shown as examples in FIG. 4) using the same frequency band and with different reception field strengths (received power) are superimposed. The receiving station demodulates the signal with the highest reception power (signal 1 in FIG. 4). Next, the receiving station generates a replica signal of signal 1 and removes signal 1 from the superimposed signal. This results in signal 2.

[0025] The terminal 10a receives the signals shown in Figure 3C at S1 and S2. The terminal 10a receives an instruction from the base station 1A (satellite station 2A) to demodulate the signal at S1. The terminal 10a demodulates the superimposed signal at S1 (demodulation and decoding in accordance with the modulation and coding scheme (MSC)) to obtain data addressed to the terminal 10a (downlink user data). Meanwhile, the terminal 10b receives the signals shown in Figure 3D at S1 and S2. The terminal 10b receives an instruction from the base station 1B (satellite station 2B) to demodulate the signal at S2. The terminal 10b demodulates the superimposed signal at S2 (demodulation and decoding in accordance with the MSC) to obtain data addressed to the terminal 10b.

[0026] 5A and 5B are explanatory diagrams of the demodulation method of the OCC continuous transmission signal in the terminals 10A and 10B. In FIG. 5A, the terminal 10A uses the SIC described with reference to FIG. 4 to remove the signal addressed to the terminal 10a from the signal received at S1 and remove the signal addressed to the terminal 10b from the signal received at S2. As a result, the OCC continuous transmission signal addressed to the terminal 10A and the OCC continuous transmission signal addressed to the terminal 10B remain as residual signals. The terminal 10A performs S1+S2 processing on the residual signal, i.e., adds the residual signal of S2 to the residual signal of S1, leaving only the OCC continuous transmission signal addressed to the terminal 10A. By combining these, a signal addressed to the terminal 10A with increased reception power is obtained. The signal is demodulated and decoded in accordance with the MSC to obtain data addressed to the terminal 10A. The processing of S1+S2 (signal calculation method) is performed according to instructions from the base station 1A (satellite station 2A).

[0027] Similarly, in Fig. 5B, terminal 10B uses the SIC described with reference to Fig. 4 to remove the signal addressed to terminal 10a and the signal addressed to terminal 10b to obtain a residual signal. Terminal 10A performs S1-S2 processing on the residual signal, i.e., subtracts the residual signal S2 from the residual signal S1, leaving only the OCC serial transmission signal addressed to terminal 10B, and by combining these, a signal addressed to terminal 10B with increased reception power is obtained. This signal is demodulated and decoded in accordance with the MSC, thereby obtaining data addressed to terminal 10B. The S1-S2 processing (signal calculation method) is performed in accordance with instructions from base station 1B (satellite station 2B).

[0028] 6A, 6B, and 6C are diagrams showing examples of transmit power control (TPC) in continuous transmission using OCC. Fig. 6A shows a transmit signal (a signal for downlink communication) from satellite station 2A that has undergone transmit power control, and Fig. 6B shows a transmit signal (a signal for downlink communication) from satellite station 2B that has undergone transmit power control. Fig. 6C is an explanatory diagram of demodulation processing in terminal 10A (10B).

[0029] The transmission power of the OCC serial transmission signal may differ between timings (slots) and between terminals 10. In the example shown in Fig. 6A, the transmission power in S1 is set lower than the transmission power in S2, and vice versa in Fig. 6B. The terminal 10 can control the transmission power, i.e., set the transmission power, in accordance with instructions from the base station 1 (satellite station 2).

[0030] Figure 6C shows signals received by terminal 10A (10B), and terminal 10A (10B) can remove signals addressed to terminals 10a and 10b using SIC. Among the residual signals obtained by the removal, for example, a signal at S1 with low received power can be amplified to match the received power of the signal at S2, thereby aligning the received power (signal level) of the signal at S1 and the signal at S2. Terminal 10A (10B) can then obtain the signal addressed to itself by performing the processing described using Figure 5A or Figure 5B. Terminal 10A (10B) can then obtain data addressed to terminal 10A (10B) by demodulating and decoding the signal according to MSC.

[0031] FIG. 7 illustrates a hardware configuration of a wireless device applicable to the base station 1, satellite station 2, or terminal 10. The wireless device 100 includes a CPU 11, a main memory device 12, and external devices, all interconnected via a bus 17, and executes communication and information processing using a computer program. The CPU 11 is also referred to as a processor. The CPU 11 is not limited to a single processor and may be configured as a multiprocessor. The CPU 11 may also include a graphics processing unit (GPU), a digital signal processor (DSP), or the like. The CPU 11 may also cooperate with a hardware circuit such as a field programmable gate array (FPGA). Examples of external devices include an external memory device 13, an output device 14, an operation device (input device) 15, and a communication device 16, as shown in FIG. 7 .

[0032] The CPU 11 executes a computer program executable in the main memory device 12, causing the wireless device 100 to operate as a base station 1 or a terminal 10. The main memory device 12 stores the computer program executed by the CPU 11, data processed by the CPU 11, etc. The main memory device 12 is, for example, a dynamic random access memory (DRAM), a static random access memory (SRAM), a read-only memory (ROM), etc. The external memory device 13 is used as a storage area supporting the main memory device 12 and stores the computer program executed by the CPU 11, data processed by the CPU 11, etc. The external memory device 13 is, for example, a hard disk drive, a solid state drive (SSD), etc. Furthermore, a drive device for a removable storage medium may be connected to the wireless device 100. The removable storage medium may be, for example, a Blu-ray disc, a digital versatile disc (DVD), a compact disc (CD), a flash memory card, etc.

[0033] The output device 14 is, for example, a display device such as a liquid crystal display or an electroluminescence panel. However, the output device 14 may also include a speaker or other device that outputs sound. The operation device 15 is, for example, a key, button, dial, or touch panel with a touch sensor overlaid on a display. The communication device 16 communicates with the base station 1 and an external network such as the Internet via, for example, optical fiber. The communication device 16 includes a wireless communication device (including a transmitting / receiving antenna) used for wireless communication between the base station 1 or satellite station 2 and the terminal 10, and a communication device for the base station 1 to communicate with the core network. The communication device 16 may also include communication equipment for connecting to a wireless LAN (Wi-Fi). The communication device 16 may be a single device or a combination of multiple devices.

[0034] The processes executed by the CPU 11 and memory (e.g., main storage device 12) may be executed by semiconductor devices such as FPGA, CPLD (Complex Programmable Logic Device), ASIC (Application Specific Integrated Circuit), SoC (System on a chip), etc. The CPU 11 (processor), FPGA, CPLD, ASIC, and SoC are examples of "circuitry" included in a wireless device operable as the base station 1 or the terminal 10.

[0035] 8 is a sequence diagram showing an example of message exchange between a base station and a terminal 10. The satellite station 2 intervening between the base station 1 and the terminal 10 is omitted.

[0036] When the RRC (Radio Resource Control) state of the terminal 10 is an idle state or an inactive state, the base station 1 transmits paging information to the terminal 10 using a paging channel (PCH) (<1> in FIG. 8). Then, information is exchanged between the terminal 10 and the base station 1 to transition the RRC state to an RRC connected state (<2> in FIG. 8).

[0037] When the RRC state of the terminal 10 transitions to the RRC connected state, the base station 1 transmits a channel state information (CSI) request to the terminal 10 using the physical downlink control channel (PDCCH) if necessary for scheduling (<3> in FIG. 8). The terminal 10 generates information including the channel state information (CSI information) and transmits it to the base station 1 using the physical downlink shared channel (PDSCH) (<4> in FIG. 8).

[0038] Thereafter, the control station 3 or the base station 1 performs scheduling for downlink communication of the terminal 10. The base station 1 transmits scheduling information to the terminal 10 using the PDCCH (<5> in FIG. 8). The base station 1 transmits data (user data) to be used for downlink communication to the terminal 10 using the PDSCH (<6> in FIG. 8). The terminal 10 transmits an ACK or NACK (Negative Acknowledgement) message using the Physical Uplink Control Channel (PUCCH) or the Physical Uplink Shared Channel (PUSCH) (<7> in FIG. 8).

[0039] When the base station 1 receives the NACK, the base station 1 transmits retransmission control information to the terminal 10 using the PDCCH (<8> in FIG. 8). After that, the base station 1 transmits retransmission data to the terminal 10 using the PDSCH (<9> in FIG. 8).

[0040] 9 is a sequence diagram showing the operation of the communication system. The control station generates information on the interference area (FIG. 2) (FIG. 9<1>) and transmits it to the base stations 1A and 1B (FIG. 9<1A>, <1B>).

[0041] When the base station 1A desires to transmit data (downlink communication) to subordinate terminals 10A(A) and 10a(α) located in the interference area, it transmits a scheduling request of the terminals 10A and 10a, information about the terminals 10A and 10a, and information indicating the transmittable power of the base station 1A (satellite station 2A) to the control station 3 (FIG. 9<2A>). The information about the terminals 10A and 10a includes information indicating the CSI, data volume, priority, allowable delay time, and link budget between each terminal.

[0042] When the base station 1B desires to transmit data (downlink communication) to subordinate terminals 10B(B) and 10b(β) located in the interference area, it transmits the scheduling requests of the terminals 10B and 10b, information about the terminals 10B and 10b, and information indicating the transmittable power of the base station 1A (satellite station 2A) to the control station 3 (FIG. 9<2B>). The information about the terminals 10B and 10b includes information indicating the CSI, data volume, priority, allowable delay time, and link budget between each terminal.

[0043] The control station 3 schedules data transmission to the terminals 10A and 10a and the terminals 10B and 10b (Fig. 9<3>). As a result of the scheduling, the control station 3 transmits to the base station 1A information indicating destination terminals (transmission-permitted terminals) that are permitted to transmit data among the terminals 10 that requested scheduling, and schedule information (Fig. 9<4A>). The schedule information includes information indicating the allocation of radio resources to each transmission-permitted terminal, information indicating the allocation of transmission power to each transmission-permitted terminal, NOMA information (whether a signal is superimposed on an OCC repetitive transmission signal), whether OCC is applied, and parameters when OCC is applied (number of repetitive transmissions, OCC pattern, etc.).

[0044] Furthermore, the control station 3 transmits information on the transmission-permitted terminals and schedule information to the base station 1B as a result of scheduling (Fig. 9<4B>). The schedule information includes information indicating the allocation of radio resources to each transmission-permitted terminal, information indicating the allocation of transmission power to each transmission-permitted terminal, NOMA information (whether a signal is superimposed on an OCC repetitive transmission signal), whether or not to apply OCC, and parameters when applying OCC (number of repetitive transmissions, OCC pattern, etc.).

[0045] Based on information indicating the transmission-permitted terminals and schedule information, the base station 1A transmits control information such as resource allocation to the terminals 10A and 10a using the PDCCH (Fig. 9<5A>). Based on information indicating the transmission-permitted terminals and schedule information, the base station 1B transmits control information such as resource allocation to the terminals 10B and 10b using the PDCCH (Fig. 9<5B>). Thereafter, the base station 1A transmits data to be used for downlink communication to the terminals 10A and 10b using the PDSCH (Fig. 9<6A>). Furthermore, the base station 1B transmits data to be used for downlink communication to the terminals 10B and 10a using the PDSCH (Fig. 9<6B>). The control station 3, the base station 1A, the satellite station 2A, the base station 1B, and the satellite station 2B operate in synchronization so as to share radio resources.

[0046] Fig. 10 is a diagram showing an example of the configuration of the base station 1. The wireless device 100 shown in Fig. 7 can operate as the base station 1 having the configuration shown in Fig. 9 by the CPU 11 executing a program.

[0047] 10, base station 1 includes radio protocol control unit 201 having scheduler 202, PDCCH / PCH control unit 203, radio unit 204, antenna 205, and control unit 206. Satellite station 2 includes at least an antenna for transmitting and receiving radio waves, a radio unit, and a mechanism for amplifying the transmitted and received radio waves (modifying the signal waveform).

[0048] The scheduler 202 communicates with the control station 3 and can identify the terminals 10 (terminals 10A and 10a) located in the interference area using interference area information from the control station 3 and location information of the subordinate terminals 10. The scheduler 202 transmits scheduling requests and the like from each terminal 10 to the control station 3 (Figs. 9<2A>, 9<2B>). It also receives information on terminals permitted to transmit and their schedule information from the control station 3 (Figs. 9<4A>, 9<4B>).

[0049] The scheduler 202 sends a control signal to each terminal 10, which includes a radio resource instruction (information indicating the allocation of radio resources), OCC designation information (number of consecutive transmissions (= 2, 4, 8, 16, ...), OCC pattern, and content of transmission power control), and NOMA information (information on whether signals are superimposed).

[0050] The PDCCH / PCH control unit 203 performs a process of transmitting paging information to the terminal 10 using the PCH, and a process of mapping a control signal from the radio protocol control unit 201 onto the PDCCH and transmitting it to the terminal 10. The radio unit 204 converts the output signals (baseband signals) of the PDCCH / PCH control unit 203 and the control unit 206 into radio signals (radio waves). The antenna 205 is a transmitting / receiving antenna that emits radio waves from the radio unit 204 and sends received radio waves to the radio unit 204. The radio unit 204 performs a process of converting the radio waves into baseband signals. Channel state information (CSI) and ACK / NACK messages in the baseband signals are sent to the scheduler 202.

[0051] The scheduler 202 receives data (transmission data) to be transmitted via downlink communication from a higher layer. The transmission data is converted into a transmission data signal by modulation and encoding according to the MCS in the radio protocol control unit 201, and is then provided to the control unit 206. The control unit 206 maps the transmission data signal addressed to each terminal 10 onto the PDSCH (signal generation) in accordance with control signals (radio resource instruction, OCC designation, NOMA information) so that the signal shown in FIG. 2A (FIG. 2B) is transmitted from the satellite station 2A (2B). The control unit 206 can also control transmission power according to the TPC information by controlling the radio unit 204.

[0052] FIG. 11 is an explanatory diagram of OCC and transmission power control. FIG. 11 illustrates four types of OCC and transmission power instruction patterns when the number of consecutive transmissions is 4. Patterns 1 to 4 have different OCC code patterns. Also, patterns 1 to 4 illustrate an example in which the transmission power in the second transmission (continuous transmission index number = 2) in consecutive transmissions is reduced by -3 dB (difference = -3 dB) compared to the normal transmission power. In the first, third, and fourth transmissions (continuous transmission index numbers = 1, 3, 4), the difference from the normal transmission power is 0 dB. Information indicating the value of the transmission power at each transmission (timing) can also be transmitted as a transmission power instruction.

[0053] Fig. 12 is a diagram showing an example of the configuration of the terminal 10. When the CPU 11 executes a program, the wireless device 100 shown in Fig. 7 operates as the terminal 10 including a radio protocol control unit 101, a PDCCH / PCH control unit 102, a radio unit 103, an antenna 104, a PUCCH / PUSCH control unit 105, and a PDSCH control unit 106.

[0054] In FIG. 12 , antenna 104 is a transmitting / receiving antenna for transmitting and receiving radio waves. Radio unit 103 converts between radio waves (radio signals) and baseband signals. PDCCH / PCH control unit 102 acquires paging information mapped to the PCH, control information (including schedule information) mapped to the PDCCH, and retransmission control information, and passes them to radio protocol control unit 101. Radio protocol control unit 101 can output information for transitioning the RRC state to a connected state and CSI information. The information for transitioning the RRC state to a connected state and CSI information are mapped to the PUCCH in PUCCH / PUSCH control unit 105, and transmitted from antenna 104 via radio unit 103. ACK / NACK messages transmitted from radio protocol control unit 101 are also transmitted from antenna 104 via PUCCH / PUSCH control unit 105 and radio unit 103.

[0055] A radio signal including target data for downlink communication received by antenna 104 is provided to PDSCH control unit 106 via radio unit 103. The PDSCH control unit can perform demodulation using SIC, demodulation using OCC information, and demodulation and decoding using MCS in accordance with schedule information provided by radio protocol control unit 101. As a result, the original data is obtained and passed from radio protocol control unit 101 to a higher layer.

[0056] Fig. 13 is a flowchart showing an example of processing by the control station 3. The control station 3 has, for example, a configuration similar to the hardware configuration of the wireless device 100 shown in Fig. 7 (however, the communication device is a wired communication device), and can perform the processing shown in Fig. 13 by the CPU 11 executing a program.

[0057] In step S201, the control station 3 notifies the interference area (<1A> and <1B> in FIG. 9). In step S202, the control station 3 receives scheduling requests and terminal information from the base stations 1A and 1B (<2A> and <2B> in FIG. 9).

[0058] In step S203, the control station 3 allocates wireless resources and power and schedules data transmission to each terminal 10 (<3> in FIG. 9). In step S204, the control station 3 transmits information on terminals permitted to transmit and schedule information to the base stations 1A and 1B (<4A> and <4B> in FIG. 9).

[0059] 14 is a flowchart showing an example of processing by a base station. In step S01, the base station 1 detects the generation of data to be transmitted in downlink to the terminal 10. In step S02, the base station 1 determines whether the RRC state of the terminal 10 is in a connected state. If it is determined that the RRC state is in a connected state, the processing proceeds to step S03; otherwise, the processing proceeds to step S04.

[0060] In step S03, the base station 1 determines whether or not it has valid CSI for the terminal 10. If it is determined that valid CSI is available, the process proceeds to step S06; otherwise, the process proceeds to step S05.

[0061] In step S04, the base station 1 performs a process of transitioning to an RRC connected state, and then proceeds to step S06. In step S05, the base station 1 performs a process of acquiring CSI from the terminal 10, and then proceeds to step S06.

[0062] In step S06, the base station 1 transmits a scheduling request to the control station 3 (FIGS. 9<2A> and 9<2B>). In step S07, the base station 1 uses the transmission permission terminal information and schedule information received from the control station 3 to schedule radio resources, power allocation, and the like related to downlink communication of the terminal 10.

[0063] In step S08, the base station 1 transmits control information (radio resource allocation, OCC instruction, transmission power instruction, etc.) using the PDCCH. In step S09, the base station 1 transmits signals (OCC serial transmission signals, NOMA signals) in which data addressed to the terminal 10 is modulated in accordance with the MCS, using the PDSCH.

[0064] In step S09, the base station 1 determines whether or not an ACK message has been received from the terminal 10. If it is determined that an ACK message has been received, the processing of Fig. 14 is completed, and if not, retransmission control is performed (step S11).

[0065] 15 is a flowchart showing an example of processing by the terminals 10A and 10B. In step S101, the terminal 10A (10B) in the RRC connected state waits for received data (reception of data for downlink communication). If the RRC state of the terminal 10A (10B) is not the RRC connected state, a transition process to the RRC connected state (steps S111 to S113) is performed.

[0066] In step S102, the terminal 10A (10B) receives a PDCCH, i.e., receives information necessary for demodulation such as radio resource allocation, OCC instructions, etc. In step S103, the terminal 10A (10B) receives a PDSCH, i.e., receives data for downlink communication.

[0067] In step S104, the terminal 10A (10B) performs interference cancellation of the NOMA signal using SIC (see FIGS. 4, 5A, and 5B). In step S105, the terminal 10A (10B) performs OCC demodulation (see FIGS. 5A and 5B).

[0068] In step S106, the terminal 10A (10B) performs demodulation in accordance with the MCS to obtain demodulated data. In step S107, the terminal 10A (10B) determines whether the demodulated data is error-free. If it is determined that the demodulated data is error-free, the demodulated data is sent to a higher layer; if not, data retransmission control is performed (step S108).

[0069] Fig. 16 is a flowchart showing an example of processing by the terminals 10a and 10b. The example of processing shown in Fig. 16 differs from the processing in Fig. 15 in that steps S104 and S105 shown in Fig. 15 are not included, but other than this, the processing is the same as the processing in Fig. 15. In step S106, the terminal 10a (10b) performs demodulation based on the MCS of the signal mapped to the radio resource (RB) specified in the radio resource allocation, thereby obtaining demodulated data.

[0070] According to a communication system and a wireless communication control method according to an embodiment, a transmitting station (satellite station 2A (22B)) connected to a first wireless terminal (terminal 10A (10B)) belonging to a first group and a second wireless terminal (terminal 10a (10b)) belonging to a second group different from the first group transmits a first signal (OCC repetitive transmission signal) to the first wireless terminal (terminal 10A (10B)) at multiple timings (e.g., slots) using an orthogonal cover code (OCC repetitive transmission). The transmitting station (satellite station 2A (22B)) can also transmit a second signal (NOMA signal) to the second wireless terminal (terminal 10a (10b)) at a specific timing among the multiple timings. The transmission power of the first signal (OCC repetitive transmission signal) on which the second signal (NOMA signal) is superimposed can be configured to be lower than the transmission power of the second signal (NOMA signal). A configuration can be adopted in which the transmission power of the second signal (NOMA signal) and the first signal (OCC serial transmission signal) on which the second signal is superimposed is determined so that the second signal (NOMA signal) and the first signal (OCC serial transmission signal) on which the second signal is superimposed have a predetermined signal-to-interference power ratio (SIR). This ensures that the signal transmitted from the satellite station 2A (2B) to the terminals 10A and 10a (10B and 10b) has the SIR required for SIC. Furthermore, the transmitting station (satellite station 2A (2B)) can control (increase or decrease) the transmission power at multiple timings. From the perspective of achieving the above advantages, the communication system does not need to have a system for the base station 1A (base station 1A, satellite station 2A, terminals 10A and 10a) and a system for the base station 1B (base station 1B, satellite station 2B, terminals 10B and 10b), and only needs to have one of the systems.

[0071] However, as shown in Figures 1 and 2, the communication system can adopt a configuration in which a second transmitting station (satellite station 2B) different from the first transmitting station (satellite station 2A), which is a transmitting station, transmits a third signal (OCC continuous transmission signal) by continuous transmission using an orthogonal cover code to a first wireless terminal (terminal 10B) connected to the second transmitting station (satellite station 2B) at multiple timings.

[0072] The second transmitting station (satellite station 2B) may transmit a fourth signal (NOMA signal) superimposed on a third signal (OCC serial transmission signal) transmitted at a timing other than the specific timing among the plurality of timings to a second wireless terminal (terminal 10b) connected to the second transmitting station (satellite station 2B). This allows wireless resources (frequency bands) to be shared between the transmitting stations, improving frequency utilization efficiency. In this case, a configuration may be adopted in which the transmission power of the third signal superimposed on the fourth signal is lower than that of the fourth signal. Also, a configuration may be adopted in which the transmission power of the fourth signal and the first signal superimposed on the fourth signal are determined so that the fourth signal and the third signal superimposed on the fourth signal have a predetermined signal-to-interference power ratio. The second transmitting station may control the transmission power at the plurality of timings.

[0073] The communication system according to the embodiment employs a configuration in which the link budget value of a first wireless terminal (terminals 10A and 10B) belonging to a first group is better than the link budget value of a second wireless terminal (terminals 10a and 10b) belonging to a second group. However, the criterion for dividing the first and second groups may be other than the link budget value. Furthermore, the communication system according to the embodiment illustrates a case in which the first wireless terminal and the second wireless terminal are located in an overlapping area (interference area) between the coverage area of ​​the first transmitter station and the coverage area of ​​the second transmitter station. However, a downlink communication signal in which an OCC serial transmission signal and a NOMA signal are superimposed may be transmitted to multiple terminals located in a coverage area other than the interference area of ​​the satellite station 2A (2B).

[0074] The above-described embodiment is merely an example, and the present disclosure may be modified as appropriate within the scope of the present disclosure. Furthermore, the processes and means described in the present disclosure may be freely combined and implemented as long as no technical contradiction occurs.

[0075] Furthermore, a process described as being performed by one device may be shared and executed by multiple devices. Alternatively, a process described as being performed by different devices may be executed by a single device. In a computer system, the hardware configuration (server configuration) by which each function is realized can be flexibly changed.

[0076] The present disclosure can also be realized by supplying a computer program that implements the functions described in the above embodiments to a computer, and having one or more processors in the computer read and execute the program. Such a computer program may be provided to the computer on a non-transitory computer-readable storage medium connectable to the computer's system bus or via a network. Non-transitory computer-readable storage media include any type of medium suitable for storing electronic instructions, such as any type of disk, including magnetic disks (e.g., floppy disks, hard disk drives (HDDs), etc.), optical disks (e.g., CD-ROMs, DVDs, Blu-ray disks), read-only memory (ROM), random access memory (RAM), EPROM, EEPROM, magnetic cards, flash memory, or optical cards.

Claims

1. A wireless communication control method comprising: a transmitting station connected to a first wireless terminal belonging to a first group and a second wireless terminal belonging to a second group different from the first group, transmitting a first signal to the first wireless terminal, the first signal being transmitted at multiple timings by continuous transmission using an orthogonal cover code; and the transmitting station transmitting a second signal to the second wireless terminal, the second signal being superimposed on the first signal transmitted at a specific timing among the multiple timings.

2. The wireless communication control method according to claim 1, wherein the transmission power of the first signal on which the second signal is superimposed is lower than the transmission power of the second signal.

3. The wireless communication control method according to claim 2, wherein the transmission power of the second signal and the first signal on which the second signal is superimposed is determined so that the second signal and the first signal on which the second signal is superimposed have a predetermined signal-to-interference power ratio.

4. The wireless communication control method according to claim 1, wherein the transmitting station controls the transmission power at the plurality of timings.

5. The wireless communication control method according to claim 1, further comprising a second transmitting station different from the first transmitting station transmitting a third signal by continuous transmission using an orthogonal cover code to the first wireless terminal connected to the second transmitting station at the plurality of timings.

6. The wireless communication control method according to claim 5, wherein the second transmitting station transmits, at a timing other than the specific timing among the plurality of timings, a fourth signal superimposed on the third signal transmitted at the timing other than the specific timing among the plurality of timings, to the second wireless terminal connected to the second transmitting station.

7. The radio communication control method according to claim 6, wherein the transmission power of the third signal on which the fourth signal is superimposed is lower than the transmission power of the fourth signal.

8. The wireless communication control method according to claim 7, wherein the transmission power of the fourth signal and the first signal on which the fourth signal is superimposed is determined so that the fourth signal and the third signal on which the fourth signal is superimposed have a predetermined signal-to-interference power ratio.

9. The wireless communication control method according to claim 6, wherein the second transmitting station controls the transmission power at a plurality of timings.

10. A wireless communication control method according to claim 1, wherein the link budget value for the first wireless terminal belonging to the first group is better than the link budget value for the second wireless terminal belonging to the second group.

11. The wireless communication control method according to claim 5, wherein the first wireless terminal and the second wireless terminal are located in an overlapping area between the coverage area of ​​the first transmitting station and the coverage area of ​​the second transmitting station.

12. A communication system including a transmitting station connected to a first wireless terminal belonging to a first group and a second wireless terminal belonging to a second group different from the first group, wherein the transmitting station performs the following processes: transmitting, to the first wireless terminal, a first signal transmitted at multiple timings by continuous transmission using an orthogonal cover code; and transmitting, to the second wireless terminal, a second signal superimposed on the first signal transmitted at a specific timing among the multiple timings.

13. The communication system according to claim 12, wherein the transmission power of the first signal on which the second signal is superimposed is lower than the transmission power of the second signal.

14. The communication system according to claim 13, wherein the transmission power of the second signal and the first signal on which the second signal is superimposed is determined so that the second signal and the first signal on which the second signal is superimposed have a predetermined signal-to-interference power ratio.

15. The communication system according to claim 12, wherein the transmitting station controls the transmission power at the plurality of timings.

16. The communication system according to claim 12, further comprising a second transmission station different from the first transmission station, wherein the second transmission station transmits a third signal by continuous transmission using an orthogonal cover code to the first wireless terminal belonging to the first group connected to the second transmission station at the plurality of timings.

17. The communication system described in claim 16, wherein the second transmitting station transmits, at a timing other than the specific timing among the plurality of timings, a fourth signal superimposed on the third signal transmitted at the timing other than the specific timing among the plurality of timings, to a second wireless terminal belonging to the second group connected to the second transmitting station.

18. The communication system according to claim 17, wherein the transmission power of the third signal on which the fourth signal is superimposed is lower than the transmission power of the fourth signal.

19. The communication system according to claim 18, wherein the transmission power of the fourth signal and the first signal on which the fourth signal is superimposed is determined so that the fourth signal and the third signal on which the fourth signal is superimposed have a predetermined signal-to-interference power ratio.

20. The communication system according to claim 19, wherein the second transmitting station controls the transmission power at a plurality of timings.

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